Technology under the TouchScreen
Day by day, work becomes simple due to the important role played by scientists and engineers. Most of them do their inventions to make our work simple and easy. As a substitute to the old keypad of the mobile phone they invented the screen sensor which can detect the user's input directly without letting them move with the old arrow keys. They used the five-wire resistive technology which was developed and patented by Elographics in 1977. In recent years this technology has became more familiar after the invention of Apple's iphone.
After this inventory most people thought they invented a new gadget which can display and detect the human touches on the same surface. But actually as same as the old models, touch screen model phones also had the old LCD display screen. The new inventory was the glass plate called digitizer which was pasted over the surface of LCD display.
This separate transparent plate can detect human touches without any semi conductible compounds. It contains a massive concept mastered in digital electronics.. They used three special systems in parallel to detect these sensors. This technology they used in each system to detect human touches is very interesting.
Digitizer is device that converts analog information into a digital form. It contains three main systems to identify the user's input. They can be found in different ways in several technologies. These touch responses from the user can be catch by using a Resistive Sensor, Capacitive sensor or a Surface acoustic wave sensor.
- Resistive sensor's operation
This method is mostly uses technology in year 2005 to 2008 end in many and most mobile phones and other touch sensitive devices. This resistive system consists of a normal glass layer that is covered by a transparent conductive and a resistive metallic layer. There is a small gap between these two layers. Another tiny plate is there on the top of this whole setup for its protection. That layer is made of scratch free materials. In modern devices this can be found as an extra option with scratch free 'Corning Gorilla Glass'.
When the back-light of the LCD screen is turn on, this digitizer becomes active automatically . At the same time, a small electrical current flows through these above mentioned two layers. Every time, the user touches the screen, these two layers make contact in that exact point. The change in the electrical field is transmitted to the main board of the device as a digital signal. Main processor of the device is used to catch these signal and give the relevance response for the each touch.
- Capacitive sensor's operation
In a capacitive type touch screen has a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the display with his or her finger, some of the charge is transferred to the user, thus the charge on the capacitive layer decreases. To measure this decrement, it also transfers a digital signal to the main board. This signal is also analyzed by another class file located in the firmware. This capacitive system is more reliable than the resistive system, because it transfers only the coordinates of the position. It cannot transfer a long press in the same position. Both resistive system and capacitive system can be damaged by a hard touch from a user. The advantage of this capacitive type touch screens is that they only response for human touches because it deals with the charge current in human body. But in resistive type screens it came with plastic stylus. We can't use the styluses in capacitive type touchscreens and we have to use dedicated styluses for capacitive digitizers.
- Surface acoustic wave system
On the display there is another modern system runs to deliver the exact position by using two transducers. One is for receiving and other one for sending. Both are placed along the x
and y axes of the digitizer's glass plate. Also there are glass reflectors to turn the electronic signal from one to another. On each wave transferring moment if any disturbance happens to the wave it can instantly detect by the receiving transducer. This works much alike the resistive system. Because this also allows the user to detect a touch from any object. But some mobile phone companies don't use this technology for their products because it costs too high. This technology is very useful for special effects on touchscreens like finger tracking and to compare multi touch variations.
Finally, manufactures use a calibration part in its software to set the digitizer positions to match with the variables in the main firmware. These coordinates of the exact point of contact are calculating in the mobile firmware program which runs in the device. Once the coordinates are known, another class is used to convert the coordinates into an output that main firmware can understand, in a similar way a keypad or a joystick button functions. In the latest devices announced after the year 2010 they mostly use capacitive type touch screens because they are more sensitive and user friendly than traditional resistive touchscreens.
Hope this article will be an interesting one for those who are enthusiastic in electronics and technology ...!!! ;-)
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